Steering back to the Space Wolves thoughts...
Wolves (on Earth) mate after about 2-3 years, with a lifespan around 5-6 years. So, the first third of their life they start reproducing.
If lifespan in the 40k universe is shorter due to how grimdark things are (say 40), then yes I can see reproducing earlier. Heck even now it's not uncommon for teens to be with child.
With respects to the body hair, there are no wolves on Fenris...